Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

114
FXUS63 KLOT 082327
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
627 PM CDT Wed Jul 8 2026

.KEY MESSAGES...

- Thunderstorm chances return Thursday, with the potential for
  localized heavy rainfall Thursday afternoon and evening.
  Strongest storms may also be capable of localized gusty winds,
  mainly south of I-80.

- Mainly dry, warmer weather expected this weekend into early
  next week.

&&

.DISCUSSION...
Issued at 237 PM CDT Wed Jul 8 2026

A warm, dry afternoon is underway across the forecast area as
an area of weak surface high pressure drifts slowly southeast of
the cwa. A few showers and isolated thunderstorms were noted
across southeast WI, where west-southwesterly return flow has
brought a return of low-70s surface dew points, though drier
low-levels and warmer mid-level temps across our local area
should provide enough of a cap to minimize any convective threat
here for the remainder of the afternoon/evening. Shower and
thunderstorm chances are expected to increase across northern IL
toward daybreak Thursday however, as an area of thunderstorms
currently developing across IA/MN/WI eventually approaches the
area. High-res CAM guidance continues to be in good agreement
that this area of convection will be in a weakening/decaying
mode by that time, though may push an outflow boundary into the
area after 1-3 AM. Given the diurnal instability minima during
the early morning, guidance is not very excited about convective
development along the remnant outflow, though isolated to
widely-scattered showers and perhaps an isolated thunderstorm
are possible generally along/north of the I-88 corridor
especially by late morning as daytime warming eventually
destabilizes the boundary layer.

Scattered thunderstorm chances do increase from midday Thursday
into the evening, as the synoptic cold front slowly pushes
southeast into the forecast area along with some support from an
approaching mid-level short wave. This wave appears weaker than
some model runs had been depicting over the past few days,
resulting in weaker mid-level westerly flow (20-25 kts as
opposed to ~40 kts in some runs previously). Overall weaker
forcing, and relatively poor forecast mid-level lapse rates,
appear to be responsible for the sparser convective footprint in
current CAM guidance across the cwa. There is still some
support in current CAM runs for a remnant MCV (from an MCS
forecast to develop along the NE/KS border later tonight) to
approach the area later in the afternoon/evening which looks to
yield somewhat greater shower/thunderstorm coverage during that
time. Similar to earlier runs however, the exact track (while
perhaps a bit south of previous forecasts) remains of somewhat
lower confidence. In any case, these slow-moving storms will
provide a threat of heavy rainfall, with localized amounts of
1-2" possible. Weaker mid-level flow (Corfidi propagation
vectors potentially 5-10 mph to the ESE), precipitable water
values approaching 2" and deep warm-cloud depths all support the
likelihood of torrential downpours with some of these storms.
Soil moisture, river/creek levels and storm water retention
facilities continue to run quite high in portions of the cwa
where repeated heavy rains occurred over the past week -
especially across portions of the central and southern Chicago
metro area. This raises concern for any additional localized
heavy rainfall to potentially cause renewed flooding. With this
in mind, have collaborated with WPC to include appropriate
portions of our forecast area in their Day 2 Excessive Rainfall
Outlook in a slight (level 2 of 4) risk.

The surface cold front is progged to continue to work southeast
across the forecast area Thursday night, eventually slowing
further and becoming nearly stationary across downstate IL/IN on
Friday. This should allow showers and lingering storms to
diminish from NW to SE Thursday night, while surface high
pressure builds across the upper Midwest. Drier east-northeast
low-level flow will bring drier and more stable conditions to
much of northeast IL/northwest IN Friday, while
isolated/scattered showers and thunderstorm chances linger
mainly off to the south of I-80 during the diurnally favored
afternoon and early evening hours. Diurnal precip chances should
continue to shift south over the weekend, as the Great Lakes
surface high settles a little farther southward.

Longer-range ensemble guidance continues to depict an upper-
level ridge building eastward across the upper Midwest/western
Great Lakes region later this weekend into early/mid next week.
This looks to support a period of dry and warmer weather
conditions (highs in the low-90s in many spots) in the extended
period. Unlike last week however, current ensembles indicate
heat within a less humid air mass. As usual on the
north/northeast periphery of an upper ridge, We`ll need to
continue to monitor the potential for thunderstorm clusters to
slide into our area, especially toward the middle of next week
as a short wave is progged to rotate across Ontario and parts of
the Lakes.

Ratzer

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 627 PM CDT Wed Jul 8 2026

Forecast concerns include...

Chance of thunderstorms Thursday afternoon/evening.
Wind shift to northeast late Thursday afternoon/early evening.
Possible mvfr cigs Thursday night.

There will be a chance of showers toward daybreak Thursday
morning across northwest IL, including RFD and along the IL/WI
state line. Some of these showers may move across the terminals
during the mid/late morning hours on Thursday but overall
coverage looks to be low. This shower activity may also be in a
weakening phase.

Isolated/scattered thunderstorms are possible Thursday
afternoon into Thursday evening, but confidence is low for
coverage. Made no changes to the current prob timing but its
possible that some thunderstorms may lingering into the early
evening Thursday and timing may need refinement with later
forecasts. Lingering showers will also be possible Thursday
evening.

Ifr cigs/vis along with brief heavy rain will be possible with
any of the thunderstorms on Thursday. But there is trend for at
least scattered mvfr level clouds Thursday evening with
possible mvfr cigs Thursday night into Friday morning.

Southwest winds will continue tonight turning more westerly on
Thursday and then a cold front will shift winds to the northeast
later Thursday afternoon or early Thursday evening. The timing
of this wind shift will be dependent on thunderstorm coverage
and timing, which could push the front through faster if
coverage is more scattered during the afternoon. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Air Quality Alert until midnight CDT tonight for INZ001-INZ002-
     INZ010-INZ011.

LM...None.

&&

$$

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